Prior optical cross-connect arrangements are known that employed electro-mechanical optical switching elements as distributors and selectors.
An electrical 1xN distributor switch is an 1xN switching device which routes the signal or signals from a single input port to any one of the N output ports. An optical 1xN distributor switch is the optical analog of an electrical 1xN distributor switch where the input and output ports are optical fibers carrying one or more optical communication signals at a given wavelength or a plurality of wavelengths. Certain distributor switches may permit routing the signal from the input line to two or more of the N output ports, thus dividing the signal energy from the input line among the target output ports. This properly is called the broadcasting or bridging capability of the distributor switch.
An optical Nx1 selector switch is the optical analog of an electrical Nx1 selector switch where the input and output ports are optical fibers carrying one or more optical communication signals at different wavelengths. Certain selector switches may permit selection of more than one input port and adding (under certain rules) the signals from the selected ports. This properly is called the collection capability of the selector switch.
A number of electromechanical optical distributor and selector switches are presently available. These devices are based on mechanically moving the input and/or output fibers or utilizing various reflective or deflective optical elements to spatially direct a beam of light from the exit pupil of the input fiber and routing it to the entrance pupils of the output fibers. Clearly, these mechanical switches are slow and, in most cases, do not permit broadcast capability, a desirable feature in communication systems. In some cases, the optical loss associated with these elements is significant.
Such prior cross-connect arrangements employing electromechanical optical distributors and selectors were limited in selecting only one line at a time, their speed was slow, and their reliability was less than desirable.
Solid state wave-guide cross-connect arrangements based on lithium niobate (see for example U.S. Pat. No. 5,181,134) or indium phosphide optical switching devices are also available which solve the speed problems. The drawback involved with these optical switching devices include polarization dependence and significant optical losses. The large optical insertion losses connected with these devices soon become intolerable when such devices are concatenated.